#include <iostream>
#include <fstream>
#include <string>

using namespace std;

ofstream & open_file(ofstream & out, const string &file)
{
    out.close();
    out.clear();

    out.open(file.c_str());
    return out;
}
int main()
{
    cout << "Hello world!" << endl;
    return 0;
}
